I feel so lonely

Is there anything I can do to reduce negative feeling? I mean I find it hard to connect with people, but my job require me to talk a lot with people. I always think that everyone doesn't like me, and I really don't know how to impress them...

Try increasing you z offset!

Connecting & Just Talking are too different things, maybe if you just post load of spam you'll feel better about yourself.

A forum for 3d printing isn't gonna be a great place to solve problems of social isolation or anxiety. Hell online is a terrible place to go. People are shitty online and you don't want our advice... So to be a hypocrite:

Sounds like social anxiety. You're probably doing just fine and people think you're just another normal guy. But if this has been a chronic thing for you I suggest finding a therapist. Most brain problems like this are from false stories we tell ourselves about the world around us and it really helps to talk to someone trained in unwinding those false narratives.

Personally I'd say go find a local club or hobby group with the same interests as you. Seems you like 3d printing, go find a makerspace, model making group, roll players, or whatever. Nerds are great friends cause they usually have just as much social anxiety or worse. It's easy to be a kind among nerds. But ya being online will not help you meet people. And I'll give you the same advice my mom gave me when my best friend died: Fake it till you make it. Pretending to be happy/ distracting yourself is better than focusing on your sadness. It will just keep pulling you down.